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**chemical purity**of the materials EEStor plans to use for their capacitor is

**not the critical parameter**needed to characterize the material. The most important parameter is yield. And

**Defect Free Yield**is primarily determined by the

**killer defect density of the dielectric**. Let’s consider a dielectric purity, i.e. defect free, of 99.9998% (EEStor announced a purity of 99.92%). Consider a film that is 0.3 micron thick. A hard defect of 0.2 micron diameter would be a killer defect, i.e. it could not sustain the high local electric field and would be very leaky. Let’s assume that one in ten million impurities is a killer defect. This works out to 0.00143 killer defects per square cm.

Now find the area for a 1F capacitor with a dielectric constant of 2400 and effective thickness of 0.3 micron. If we use a Stapler yield model with this killer defect density and dielectric area, we get a yield of less than 1% for a 1F cap. A defect free yield, such as 1%, is not a manufacturable process. I don’t know the precise details of size, structure, and manufacture of EEStor caps or how purity relates to killer defects. By what this little exercise shows is that getting high yields won’t be easy.